1. Field of the Invention
The present invention relates to foundry practice and is specifically concerned with apparatus for cleaning castings of core and moulding sands, whose operation is based on an electrohydraulic effect.
The term "electrohydraulic effect" as used here and hereinbelow refers to the action exerted upon a solid body by pulse pressures generated by a high-voltage discharge in a liquid.
Accordingly, the term "electrohydroblasting" of castings denotes the breaking down of layers of core and moulding sands stuck to the surface of a casting by means of pulse discharges generated across an electrode and the casting, which are placed into a liquid, i.e. by means of an electrohydraulic effect.
The proposed electrohydroblasting apparatus is basically intended to process large castings and can be used preferably at enterprises with a piece and lot production, but in some instances, at ones with a large-lot production of castings.
The term "large casting" refers here and hereafter to castings of 100 kg to 40,000 kg and over.
2. Description of the Prior Art
Among the means intended to clean castings (especially large ones), the electrohydroblasting apparatus are distinguished by a high productivity, economic efficiency, ability to clean effectively complex-shaped castings and improved conditions of work. However, the problem of cleaning castings with the use of these apparatus remains as yet to be adequately solved.
The majority of apparatus for electrohydroblasting of castings is adapted for mass-production flow lines. Such apparatus are essentially similar in construction and comprise a bath with a liquid, a cluster of electrodes set against characteristic points of a casting, an electrode positioning mechanism and a handling means serving to remove a casting from a feeding conveyor and to feed the casting into the bath as is disclosed in U. K. Pat. No. 1,303,223.
As regards large castings, however, it is well known that no mass production thereof is required industrially, and such castings are produced either in single pieces or in small lots.
It is apparent that the electrohydroblasting apparatus of the above type are unfit for cleaning single-piece large castings, since this will necessitate re-arranging the electrode clusters and re-designing the handling means for each individual casting or lot of castings, which is labor-consuming and unjustifiably lengthens the time spent to prepare the apparatus for work.
Much more suitable for use in piece and small-lot production of large castings is an apparatus for electroblasting of castings disclosed in the USSR Inventor's Certificate No. 415,091.
This apparatus comprises a base, a bath with a liquid, mounted on the base and an electrode fixed in a means for introduction of said electrode into the bath and electrically connected to a pulse-current generator. The apparatus also comprises a means for feeding castings into the bath with a liquid, which means includes a movable platform mounted in vertical guides installed at the sides of the bath and a drive coupled with said platform through flexible pull members; said drive is a winch coupled with the platform through a cable-and-pulley system. The apparatus further comprises a loading device which includes horizontal guides consisting of a section mounted on the base and of a section mounted above the bath, and a self-propelled carriage for conveying containers with a casting (or castings) along the horizontal guides from the loading point to the section disposed above the bath and conveying them back to the unloading point. The self-propelled carriage is a three-component frame mounted on rollers and comprising two lengthwise, or side, girders each arranged along one of the guides, strictly thereabove, and only one cross girder interconnecting the ends of the side girders. The frame is of a U-shaped configuration in plan and installed so that its aperture faces the bath. The frame cross girder carries an electric drive of the rollers which move the frame along the guides. A container with a casting (or castings) is placed onto the carriage at the loading/unloading station, disposed on the guide section mounted on the base, so that its front portion bears on the side girders, and its rear portion, on the cross girder, for which purpose the container incorporates brackets with pins, recesses for said pins being provided on the carriage frame, one recess on each of the non-braced ends of the side girders and two recesses on the cross girder. Such an arrangement of the supporting members prevents twisting of the carriage side girders under the weight of the container with a casting (or castings). After the container has been placed onto the carriage, said carriage is moved along the horizontal guides to the extreme position on the section mounted above the bath in a manner to situate the points where the container rests upon the side girders beyond the end face of the horizontal guides, as otherwise the brackets with pins in the front portion of the container will rub against the horizontal guides during the subsequent lowering of said container on the platform. As the carriage reaches said position, the means for feeding castings into the bath is set into operation; the platform of the means moving underneath the carriage and lifting the container off the carriage by rests provided for this purpose on the platform. The carriage then travels back to allow thereby an unhindered lowering of the platform with the container into the bath. After the electrohydroblasting of the casting has been accomplished, the container with the casting (or castings) is by means of the platform and the carriage returned in the reverse order to the loading/unloading station.
Thus the time T of one cycle of the apparatus operation consists of the following periods:
t.sub.1 =loading time; PA1 t.sub.2 =time for conveying the container from the loading/unloading station to the position for immersing it into the bath; PA1 t.sub.3 =time for immersing the container into the bath; PA1 t.sub.4 =processing time; PA1 t.sub.5 =time for withdrawing the container out of the bath; PA1 t.sub.6 =time for conveying the container back to the loading/unloading station; PA1 t.sub.7 =time for unloading the carriage. PA1 a is the distance between the extreme points of support of one end of the crossbeam, PA1 b is the distance between the ends of the crossbeam, and .alpha. is the permissible crossbeam turning angle which sould not exceed 10 degrees of arc.
Hence, T=t.sub.1 +t.sub.2 +t.sub.3 +t.sub.4 +t.sub.5 +t.sub.6 t.sub.7, of which only t.sub.4 can be classed with productive time T.sub.p, whereas the rest of the periods fall into the unproductive or handling time T.sub.h =(T-T.sub.p)=(T.sub.1 +t.sub.2 +t.sub.3 +t.sub.4 +t.sub.5 +t.sub.6 +t.sub.7)-t.sub.4 =t.sub.1 +t.sub.2 +t.sub.3 +t.sub.5 +t.sub.6 +t.sub.7.
It is clear from the above that the productivity of the apparatus can be enhanced by shortening the processing cycle time, e.g. by reducing the handling time T.sub.h. A means to this end is to accomplish the loading/unloading operations concurrently with the processing of castings, but this is made impossible by the coincidence in space of the loading and the unloading stations, which are disposed on the guides on the same side of the bath. A next conveyor cannot thus be delivered for processing until the carriage is unloaded. On the other hand, it proves impossible to locate the loading and unloading stations on the opposite sides of the bath and to enable thereby the next container to be loaded onto the carriage while the preceding container is in the bath and the former container to be conveyed from the loading station to the bath as the latter container is transported from the bath to the unloading station because, of necessity, the guides of the apparatus are ended above the bath to permit containers to be lowered into the bath with a liquid.
Moreover, the loading device guides limit the width of the castings to be processed as those whose width exceeds the spacing (gauge) of the guides cannot pass into the bath; this narrows the processing potentialities of the apparatus (the range of products being processed).
It is an aim of the invention to provide an apparatus for electrohydroblasting of castings with loading and unloading stations located apart ensuring a higher efficiency due to a reduction in processing time obtained by performing processing and handling operations parallelly.